1. Field of the Invention
This invention relates to gas turbine combustors, and more specifically to the interface between a cap assembly and combustion chamber.
2. Description of Related Art
Gas turbine combustors typically contain at least one combustion chamber with the products of combustion directed through the aft end of the combustion chamber and into a turbine. Typically, the combustion chamber is enclosed at its forward end by a cap assembly. The cap assembly is used to deliver fuel and air from the fuel nozzles to the combustion chamber. The current cap assembly that is used in many multi-nozzle combustion chambers, which is shown in cross section in FIG. 1, has a single region for sealing the cap assembly to the combustion chamber. Cap assembly 10 contains an outer band 11 having a sealing region 12 for sealing cap assembly 10 to combustion chamber wall 13 while also fixed to wall 13 by pins 19. Depending on manufacturing tolerances and operating conditions this seal can become ineffective, resulting in an undesirable leakage of compressed air into combustion chamber 16. This leakage can alter the fuel/air ratio within combustion chamber 16, thereby affecting flame stability, and the introduction of unmixed air can adversely affect combustor emissions. Furthermore, cap assembly 10 includes an impingement plate 14 that is fixed to outer band 11 at cap assembly aft end 17 resulting in a thick and rigid joint region 15 that is directly exposed to radiation from combustion chamber 16. Although a cooling medium is permitted to flow through mixing holes 22 of impingement plate 14 and cooling holes 18, there are no holes directing a cooling medium towards joint region 15. As a result, joint region 15 can be exposed to elevated temperatures for extended periods of time, leading to premature degradation of cap assembly aft end 17.